This invention relates to refrigeration systems, and more specifically to a method and apparatus for improving the efficiency, reliability, and manufacturability of the electronic control system for an air conditioning unit.
Conventional refrigeration systems utilize a recirculating refrigerant for removing heat from a low temperature side of the refrigeration system and for discharging heat at a high temperature side of the refrigeration system. The work input necessary to operate the refrigeration system is provided by a motor driven compressor which receives low pressure gaseous refrigerant and compresses it to a high pressure. This high pressure gaseous refrigerant is supplied to a condenser where heat is removed from the gaseous refrigerant to condense it to a liquid. This liquid refrigerant is then supplied through an expansion valve to an evaporator wherein heat is transferred from a heat transfer fluid to the liquid refrigerant to evaporate the liquid refrigerant. The heat transfer fluid is thereby cooled and then used to cool a load, such as to cool a building. The evaporated refrigerant from the evaporator is returned to the compressor for recirculation through the refrigeration system. A control system directs the operation of the air conditioning unit.
The electronic control system is designed to replace the electromechanical control systems of air conditioning units. The system consists of several components: the processor board, relay board, set point board, accessory reset board, compressor protection board, control transformer, and thermistors. The processor board contains the microprocessor, power supplies, A/D converters, EXV drivers, relay drivers and display drivers. The control may use a microprocessor with an external eprom memory module or a masked version thereof.
The processor board is a generic board for use with air cooled chillers, water cooled chillers, condenserless chillers, or heat pump water to water chillers. A configuration header is used to program the control at the factory to tell the control what the physical characteristics of the particular unit are. The configuration header uses small wires that are selectively broken to configure the unit to the desired unit. The jumpers act as binary on/off switches and are used to determine the type of unit, the number of compressors, the type of expansion valve used, and the frequency of the electrical power system. The jumpers are actually located in a small header that can be removed from the board for setting the configuration. In the past the different unit configurations have been programmed into the control circuit through the control circuit wiring.
Field programmable options can be accomplished by the use of small DIP switch assemblies located on the board. The switches are generally protected by a plastic cover which must be removed before they can be changed in the field. The board also has a series of input thermistors and several switch inputs connected to it. Field adjustments of the switch set points are made through 10K ohm potentiometers.
Various outputs are controlled through relays on a relay board with a display of the outputs located on a display board. The expansion valve stepper motor, however, is controlled directly by an output from the processor board. To get the different loading sequences from the relays, the logic for controlling the relays has been stored in software and is selected by the unit configuration, compressor, and unloader jumpers. Various relays also control functions of either circuit No. 1 or circuit No. 2 compressors.
A display set point board is connected to the processor board through a ribbon cable and is used to communicate with the operator. Generally, the display set point board is located on the control/gauge panel. The board contains the leaving water set point potentiometer, a two digit display, and a display switch. Through the display, the controls show the stage of capacity, unit operation mode, and diagnostic information.
Most compressor safety controls today are initiated by flow switches which are troublesome to maintain and calibrate. Further, most refrigeration equipment uses the control circuit wiring to program the control circuit. The control wiring must be changed for each different unit manufactured. This rewiring involved a tremendous amount of time.
Ability to replace moving parts and flow switches in a control system and have a simple means to allow for the programming of a very sophisticated electronic control during the assembly of an air conditioning unit and in the field would represent a significant savings in the installation and maintenance of the unit. Thus, there exists a need for a method and apparatus which utilize electronic components to control and diagnose malfunctions in an air conditioning unit.